Interesting - it seems to be combining a variety of mechanisms to motivative people.
1. Social pressure
2. Monetary Pledges
3. Analytics
4. Group challenges.
Every fitness tracker in the market has its own approach to social motivation but they are walled gardens. (Fitbit, UP, and FuelBand have their own networks). Motivate seems to bring them together. The product right now seems heavily focused on the steps per day metric.
Another question that comes up is incentive - your friends make money when you don't accomplish your goal?
This is a hard problem to solve. I worked on something similar [1] that built on social motivation but it's clear that peer pressure alone doesn't create habits.
[1]: http://techcrunch.com/2012/08/09...